Method of sealing a glass element within a metal member



March 16, 1965 J. F. MOTSON 3,173,201

METHOD OF SEALING A GLASS ELEMENT WITHIN A METAL. MEMBER Filed Aug. 23, 1961 INVEN TOR.

JAMES F. MOTSON ww 96M,

ATTORNEY United States Patent 3,173,201 METHOD 6F SEALING A GLASS ELEMENT WITHIN A METAL MEMBER James F. Motson, 793 Welsh Road, Huntingdon Valley, Pa. Filed Aug. 23, 1961, Ser. No. 133,391 2 Claims. (62. 2473.1)

This invention relates to glass to metal seals and in particular to an end wall element to be used with hermetically sealed packages. This invention is also concerned, although its use is not restricted thereto, with the method of manufacture of an end wall element to be used with an hermetically sealed package.

Generally in furnishing glass to metal seals there are major problems involved such as: matching the coeffi cients of thermal expansion of the glass and the metal; mitigating or eliminating the strains developed in the glass; and providing a metal buffer or base that can be soldered, unsoldered and resoldered many times to the metal of the package surrounding the end wall element. For instance, end wall pieces for hermetically sealed packages, such as aircraft instruments, are generally soldered to the metal vessel or hollow cylinder holding the instrument.

Heretofore the end wall pieces, very often glass dial faces, have had a film of platinum (chemically deposited) developed around the edge thereof. The platinum film is fused to the edge of the glass at approximately 1100 F. by thermal decomposition of metal-organic platinum compounds which supply a film of platinum. At such high temperatures strains very often develop in the glass which ultimately lead to cracking the glass. In addition it has been recognized that when a platinum bead is used as the base for soldering the end wall piece to the surrounding metal, the end wall piece cannot be readily resoldered if it has had to be unsoldered. This condition is not desirable especially when an instrument becomes faulty and it is necessary to break open or unsolder the end of the instrument to make repairs.

It is therefore an object of my invention to provide an improved end wall element for hermetically sealed packages.

It is a further object of my invention to provide an end wall element which can be readily resoldered to the surrounding metal of an hermetically sealed instrument after having said end wall piece unsoldered therefrom.

In accordance with a feature of my invention a head of metal is deposited by evaporation on the edge of the end wall piece.

In accordance with another feature of my invention, in a preferred embodiment, the bead mentioned in the last feature is composed of chromium and gold.

The foregoing and other objects and features of this invention will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein FIG. 1 is a pictorial view of an hermetically sealed package with the novel end wall element;

FIG, 2 is a sectional View of FIG. 1 showing the bead and the solder bonding the glass to the metal;

FIG. 3 is a cross-section of the end wall element in a second embodiment of the invention;

FIG. 4 is a cross-section of the end wall element in a third embodiment of the invention.

FIG. 1 depicts an end wall element or end wall piece 11 of an hermetically sealed instrument package 13. The end wall element 11, in the embodiment shown in FIG. 1, includes a glass member 15. The glass member 15 is shown in FIG. 1 as an instrument dial face. Along the 3,173,201 Patented Mar. 16, 1965 ice edge of the glass member 15, as shown in FIG. 1, a bead of metal is deposited by an evaporation process. I have found that chromium when evaporated onto a glass surface adheres thereto With excellent tenacity. I have further found that gold metal as well as silver and copper metal provides an excellent base upon which to deposit solder when soldering an element to a second element of metal. Actually any solderable metal may be used, but as mentioned above chromium provides an excellent bond to glass. If, as has been done in my invention, gold metal is employed at the outer surface of the element 11 upon which the solder 19 is deposited in order to solder the end wall element 11 to the metal package 13, the element 11 can be soldered, unsoldered and resoldered many times, and each time a perfect hermetic seal is provided.

FIG. 2 is a sectional view along 2-2 of FIG. 1. As shown in FIG. 2 along the edge of the glass element 15 there is deposited (by evaporation) a head of metal 17. In a preferred embodiment the bead of metal 17 is an alloy of gold and chromium. Other metals can be evaporated on the edge of the glass element and will provide virtually all the advantages of the invention. For instance copper may be so deposited. After the bead of metal 17 has been deposited on the edge of the glass 15 the end wall element 11 is soldered by virtue of the layer of solder 19 to the metal package 13.

One of the advantages of my invention is that when the metal bead 17 is deposited by evaporation, the ambient temperatures of the glass element are in the range of only F, to F. as compared to 1100 F. when fusing a platinum bead on glass. Because of the lower ambient temperatures in an evaporation process, an end wall element of glass does not develop strains which, as mentioned above, are highly undesirable.

FIG. 3 depicts a second embodiment of my invention. In FIG. 3 there is shown a glass piece 15 upon the edge of Which is deposited by evaporation a thin film of chromium 17a upon which there is deposited, by metal evaporation, a thin film of gold 17b.

The end wall element 11 is soldered to the metal package 13 by virtue of the layer of solder 19 between the strip of gold 17b and the metal 13. By employing the gold as the outer surface it has been found that the solder can be softened thereby enabling the end wall piece 11 to be removed. The same end wall element can then be reset in the end wall position and resoldered. The procedure of unsoldering and resoldering can -be done several times and each th'ne the end wall piece is soldered to the metal package 13 a perfect hermetic seal results.

In FIG. 4 a fourth embodiment is shown. The difference between the embodiments shown in FIG. 3 and FIG. 4 is that the layer 17c is a mixture of gold and chromium. When the metal bead shown in FIG. 4 is deposited by evaporation it is done by initially depositing the chromium layer 17a, then simultaneously depositing gold and chromium forming layer and continuing to deposit gold layer 17b while terminating the deposition of chromium. I have found that the embodiment shown in FIG. 4 has remarkable strength characteristics as well as the advantages mentioned above, related to the adherence of chromium to the glass and the gold outer layer for soldering.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A method of hermetically sealing a glass end piece having first and second surfaces and a circumferential edge '3 o 4 therebetween onto the inner surface of the end of a metal ential edge; (2) and soldering said evaporated layer of package comprising the steps of (1) evaporating a metal gold and chromium to said surrounding metal member. alloy of gold and chromium onto said circumferential edge and (2) solderingsaid metal alloy to said inner sur- Referenc s Cited In the file of this patent face of the end of said metal package. 5 UNITED STATES PATENTS 2. A method of bonding a glass element having front and back surfaces and having a circumferential edge thereg 2532 between to a surrounding metal member comprising the 304171O 22? 6 a R1373 1962 steps of (1) simultaneously evaporating gold and ChI'OlTll- 3,042,550 Allen et a1 July 3, 1962 um to form a layer of metal adhering to said circumfer- 10 

1. A METHOD OF HERMETICALLY SEALING A GLASS END PIECE HAVING FIRST AND SECOND SURFACES AND A CIRCUMFERENTIAL EDGE THEREBETWEEN ONTO THE INNER SURFACE OF THE END OF A METAL PACKAGE COMPRISING THE STEPS OF (1) EVAPORATING A METAL ALLOY OF GOLD AND CHROMIUM ONTO SAID CIRCUMFERENTIAL EDGE AND (2) SOLDERING SAID METAL ALLOY TO SAID INNER SURFACE OF THE END OF SAID METAL PACKAGE. 